The invention relates generally to transmission of Internet data over a wireless communication channel. More particularly, this invention relates to transmission of Internet data using digital video broadcast format over a satellite communication channel.
Explosive growth of the Internet, including Internet related commerce, has greatly increased the demand for Internet access. This demand crosses all geographic and demographic boundaries, from developed urban neighbors and cities to remote and developing nations. Presently access to the Internet is typically through copper wire. In developed nations such infrastructure exists in the form of public telephone networks. However, in developing countries and remote locations, there may not be a copper wire infrastructure in place, and development of such an infrastructure may be excessively costly, making its development unpractical. In addition, as Internet use increases, access through existing copper wires may become unacceptably slow due to the limited bandwidth of the copper wire and increased volume of Internet traffic. Because of these and other limitations on the existing infrastructure, a high-speed, reliable Internet communication service over a satellite link is desirable. A satellite link can provide Internet access to developing countries, as well as remote locations, where there is no copper wire infrastructure in place. Moreover, Internet access over a satellite link can provide an attractive alternative to copper wire, even if the infrastructure is in place, by providing high-speed, more reliable Internet access.
The Internet is based on an architecture developed by the Defense Advanced Research Projects Agency (DARPA). This architecture is generally referred to as the transmission control protocol/Internet protocol (TCP/IP) suite. The TCP/IP protocol suite is organized into four layers: network access layer; Internet layer; TCP layer; and process layer.
FIG. 1 is a block diagram illustrating an exemplifying system for discussion of the TCP/IP model. FIG. 1 shows two nodes 20 and 22 connected to the Internet 24. As illustrated, the Internet comprises multiple subnetworks 26 and 28. Data is transferred between subnetworks through a router 30. In a node, network access layer 32 provides access to the subnetwork to which the node is connected. At the network access layer, a network header 34 is added to the data to be sent over the subnetwork. Various standards have been developed for transmission of data across subnetworks, also referred to as Local Area Networks (LAN). These standards have been collected into the Institute of Electrical and Electronic Engineers (IEEE) 802 specification. Within this specification, the IEEE 802.3 defines a LAN utilizing a carrier sense multiple access collision detection (CSMA/CD) protocol. In CSMA/CD protocol when a node on the network wants to transmit data, it senses the communication channel to determine if the channel is being used. If the channel is in use, the node does not transmit and waits for a time when no traffic is sensed to transmit. The transmitting node also monitors the channel as it transmits to determine if another node transmits at the same time. If two nodes transmit at the same time, there is a collision, which both nodes detect. Following detection of a collision, both transmitting nodes will discontinue transmission. The nodes will then wait independently random periods of time and then attempt to retransmit. A popular implementation of the CSMA/CD protocol is the Ethernet.
If data is to be transmitted between two nodes which are located on different, interconnected, subnetworks the Internet Protocol (IP) is used. At the IP layer 36, for routing across multiple networks are provided. The IP layer provides an IP header 38 which comprises the destination address. To facilitate movement of data between two subnetworks, the router 30 is used. The router 30 receives a message from one subnetwork and examines the IP header 38 for the destination address. Knowing the destination address, the router transmits the message to the appropriate subnetwork where the destination node is located.
The Transmission Control Protocol (TCP) layer 40 provides for a reliable, error free, data exchange. The TCP layer 40 receives a data block 42 from the process layer 44. If the data block 42 is too large, the TCP layer 40 divides the data block 44 into messages 46. A TCP header 48 is added to each message 46. The TCP header comprises a destination port, sequence number and checksum. The destination port identifies which port at the destination node is to receive the message 46 transmitted. The sequence number identifies the individual data packets so the messages 46 can be sequenced in the proper order at the destination node. The checksum provides a method of verifying the integrity of the data received at the destination node.
The process layer 44 contains the logic needed to support various user applications. Applications which operate on top of the TCP/IP include, for example, Simple Mail Transfer Protocol (SMTP) for basic electronic mail, File Transfer Protocol (FTP) for file transfer from one system to another, hyper text transfer protocol (xe2x80x9cHTTPxe2x80x9d) for transfer of Web pages and TELNET which provides remote login capability.
At the destination node, the process described above is performed in reverse. Traffic on the subnetwork is received by the network access layer 32. The network header 34 is removed and the remaining data passed to the IP layer 36. At the IP layer, the IP header 38 is removed and examined. If the message is addressed to the destination node, the remaining data is passed to the TCP layer 40, otherwise the message is ignored. The TCP layer removes the TCP header 48. The integrity of the message 46 is then verified using the checksum from the TCP header 48. If the data block that was sent has been divided into multiple data packets, the TCP layer 40, using the sequence number from the TCP header 48, places the messages 46 in proper order. After the TCP layer 40 has rebuilt the data block 42 that was transmitted, it passes the data block 42 to the appropriate port at the process layer 44.
While the TCP/IP and Ethernet protocols are used for transmission of data on networks such as the Internet, Digital Video Broadcast (DVB) is used to send Motion Picture Expert Group (MPEG) data over a satellite link. In the TCP/IP model, DVB would be located at the network access layer providing an interface to the physical transmission medium comprising the satellite channel.
The DVB protocol is the result of a market led consortium of public and private sector organizations in the television industry. This consortium led to the development of the DVB standard published by the European Telecommunications Standard Institute (ETSI). The DVB standard describes the modulation and channel coding system for satellite digital television broadcast. This standard is compatible with the MPEG-2 coded TV services. The MPEG-2 protocol generates digital information separated into xe2x80x9cdata pockets.xe2x80x9d DVB simply receives the data pockets and places them into xe2x80x9cdata containersxe2x80x9d for transmission over a wireless media. Within the DVB protocol, no restriction exists as to the kind of information which can be stored in these data containers.
As digital TV continues to gain acceptance and becomes common place, the demand for DVB receivers will greatly increase. Once DVB receivers come to the market in large numbers, it is expected that the commonality of design for a large market will enable costs to be kept down.
Thus, DVB can provide a cost effective means of video data transmission via satellite. However, no analogous standard, or cost effective way, has been developed to transmit TCP/IP data via satellite.
Therefore, there is a need in the technology for a means for and method of transmitting TCP/IP data over a satellite link.
Demand for high-speed, reliable Internet access is increasing. This increased demand is occurring where there is no xe2x80x9ccopper wirexe2x80x9d infrastructure in place, such as developing nations and remote areas. In addition, where the xe2x80x9ccopper wirexe2x80x9d infrasturcture is in place, its capacity is often exceeded by the demand placed upon the system. The invention provides a communication system for transmission of Internet or other TCP/IP data over a satellite link.
One embodiment provides Internet service to a plurality of remote units in communication with a satellite. The satellite is also in communication with a hub station. The hub station is further in communication with a plurality of content servers. Data from the content servers is communicated to the hub station via the Internet. The hub station then transmits the content server data received from the Internet to the plurality of remote units over the satellite link. The hub station formats the data, to be transmitted over the satellite link, in a format compatible with the DVB standard.
Further, a hub station receiving a block of Internet data for transmission to a plurality of remote units over a satellite communication channel formats the data within DVB frames such that fragment headers occur at variable locations within the DVB frame. A value, stored within the DVB frame, indicates the location of the fragment headers within the DVB frame.